Maurice Jones looks at how 3D computer-aided design can be used to increase blast efficiency
Computer-aided blast design procedures, including drill patterns, are intended to remove much of the repetitive calculation (some might say ‘guesstimation’) from the duties of the traditional shot firer in an attempt to increasing blast efficiency.
This may work very well when the task varies little, such as in uniform, stable strata using standard drilling depth, but it becomes more difficult when the operation is more difficult due to, as examples:
* Geology or structure affected by major faults, uneven jointing or unconformities;
* Mineral deposits of variable thickness;
* Variable overburden;
* Proximity of structures and communities that may be affected by vibration;
* Trials of new drill patterns, hole sizes, or explosives.
Such circumstances make the inclusion of expert knowledge at some stage of the blast design process particularly important, whether through the experience and knowledge of the mine manager, driller or shot firer; facilities built into blast design software, or the engagement of a specialist consultant. There is, after all, a vast array of data and calculations to be considered for successful blasting.
Underground mining will follow the same principles of blasting in terms of excavating the required volume to a free face and at optimum breakage, but the circumstances make achieving optimum blasting efficiency arguably more difficult with greater emphasis on:
* Smaller volumes of explosives for smaller blastholes;
* Safety of those in neighbouring workings;
* The likely need minimise overbreak;
* Smaller free space to blast into.
In both main circumstances the introduction and refinement of bulk explosives has allowed charging to more closely achieve maximum efficiency throughout the hole, as well as improving security through the less use of gelignite and related explosives.
Mike Lovitt, principal underground blasting specialist with Orica (www.oricaminingservices.com), states that bulk explosives, in emulsion phase (EP) has been a major efficiency driver for underground operations in terms of systems for delivery driving productivity and fragmentation benefits. This is shown in improvements in digging and process rates.
Generally the choice in underground mine tunnelled developments is between parallel blastholes, including larger diameter central holes to create the equivalent of another free face, or a ‘V-cut’ pattern to blast out the centre of the face first, with the aid of delay detonation. The latter case may require more drilling skill, unless automation rig controls are available, but only one bit size is necessary.
The increasing practice of larger-diameter, long hole blasting between levels throws blast calculation into another dimension, similar to open-pit mining. However, careful charging to avoid mine structure damage and excessive mineral dilution becomes even more important.
Several computer software suites used in mining, especially planning, include drill and blast design functions. For example, the drill and blast capability of the Ventyx mine planning software can be integrated with functions such as the mine geologic database (GDB) and complex stratigraphic modelling (Stratmodel). Within an interactive 3D computer-aided design (CAD) environment the software can quickly lay out an optimum blast pattern, extend the holes to the surface to form hole layout patterns. This can be given to the driller or fed into GPS-controlled drill-rigs. It also generates quick blast exclusion zones.
Blasting and mining chemicals specialist Orica offers blast design software that it has been working to improve, based on customer experience, for over 20 years. It is available as the SHOTPlus 5 software, or, for more difficult situations and blast modification, the SHOTPlus 5 Premier package. Software is also available via the company website. The Premier package includes generation of numerous report types for full feedback, and handles more complex patterns including faulted zones, irregular shapes, etc
Video 1: Dyno Nobel video highlights many of the recent innovations in underground blasting including safer bulk charging to match optimum blast design requirements
Video 2: Sequential illustrations of the removal of a ramp rock wedge from the highwall of the KCGM Superpit, Kalgoorlie, by Geovert’s geotechnical and blast team